The present invention relates to a flat-type display such as a cold cathode field emission display.
As an image display device that can be substituted for a currently mainstream cathode ray tube (CRT), flat-screen (flat-panel) displays are studied in various ways. Such flat-panel displays include a liquid crystal display (LCD), an electroluminescence display (ELD) and a plasma display (PDP). There has been also proposed a cold cathode field emission display capable of emitting electrons into a vacuum from a solid without relying on thermal excitation, a so-called a field emission display (FED), and it attracts attention from the viewpoint of the brightness of a display screen and low power consumption.
FIG. 82 shows a typical constitution of the cold cathode field emission display (to be sometimes abbreviated as xe2x80x9cdisplayxe2x80x9d hereinafter), and FIG. 83 shows a schematic exploded view of some portions of a first panel 10 and a second panel 20. In this display, the first panel (cathode panel) 10 and the second panel (anode panel) 20 are arranged to face each other and bonded to each other in their circumferential portions through a frame (not shown), so that a closed space between these two panels 10 and 20 constitutes a vacuum space. The first panel 10 has cold cathode field emission devices (to be sometimes referred to as xe2x80x9cfield emission devicexe2x80x9d hereinafter) as electron-emitting elements. FIG. 82 shows, as one example, so-called Spindt-type field emission devices each of which has electron-emitting portion 16 constituted of a conical electron emission electrode 16A. The Spindt-type field emission device comprises a stripe-shaped cathode electrode 12 formed on a support member 11, an insulating layer 13, a stripe-shaped gate electrode 14 formed on the insulating layer 13, and the conical electron emission electrode 16A formed in an opening portion 15 formed in the gate electrode 14 and the insulating layer 13. Generally, a predetermined number of such electron emission electrodes 16A having a predetermined arrangement are formed to correspond to one of phosphor layers 22 to be described later. A relatively negative voltage (scanning signal) is applied to the electron emission electrode 16A from a cathode-electrode driving circuit 34 through the cathode electrode 12, and a relatively positive voltage (video signal) is applied to the gate electrode 14 from a gate-electrode driving circuit 31. Depending upon an electric field generated by the application of these voltages, electrons are emitted from the top end of the electron emission electrode 16A on the basis of a quantum tunnel effect. The electron emission device shall not be limited to the above Spindt-type field emission device, and field emission devices of other types such as edge-type, flat-type, etc., are used in some cases.
The second panel 20 comprises a plurality of phosphor layers 22 (phosphor layers 22R, 22G and 22B) formed on a substrate 21 made, for example, of glass, the phosphor layers 22 having the form of a matrix or a stripe, a black matrix 23 filled between one phosphor layer 22 and another phosphor layer 22, and an anode electrode 24 formed on the entire surface of the phosphor layers 22 and the black matrix 23. A positive voltage higher than the positive voltage applied to the gate electrode 14 is applied to the anode electrode 24 from an anode-electrode driving circuit 37, and the anode electrode 24 works to guide electrons emitted to the vacuum space from the electron emission electrode 16A toward the phosphor layer 22. Further, the anode electrode 24 also works to protect the phosphor particles constituting the phosphor layer 22 from sputtering by particles such as ions and works to reflect light emitted by the phosphor layers 22 on the basis of electron excitation to the side of the substrate 21 to improve the brightness of a display screen observed from an outside of the substrate 21. The anode electrode 24 is made, for example, of a thin aluminum film.
Generally, the cathode electrode 12 and the gate electrode 14 are formed in the form of a stripe each in directions in which the projection images of these two electrodes 12 and 14 cross each other at right angles, and generally, a plurality of the field emission devices are arranged in an overlap region of the projection images of these two electrodes 12 and 14 (the overlap region corresponding to a region for one pixel in a monochromatic display or a region for one sub-pixel of three sub-pixels constituting one pixel in a color display). Further, such overlap regions are arranged in an effective field (region which works as an actual display screen) of the first panel 10 in the form of a two-dimensional matrix. Each pixel is constituted of a group of a predetermined number of the field emission devices arranged in the overlap region of the cathode electrode 12 and the gate electrode 14 on the first panel side and the phosphor layer 22 which is on the second panel side and faces the group of these field emission devices. The above pixels are arranged in the effective field, for example, on the order of several hundred thousands to several millions.
The first panel 10 and the second panel 20 are approximately 0.1 mm to 1 mm apart from each other. A high voltage (for example, 5 kV) is applied to the anode electrode 24 of the second panel 20. In this display, discharges sometimes take place between the gate electrode 14 formed in the first panel 10 and the anode electrode 24 formed in the second panel 20 and may impair the quality of displayed images to a great extent. The occurrence of discharges in the vacuum is considered to have the following mechanism. First, electrons or ions emitted from the electron emission electrode 16A under an intense electric field work as a trigger, the temperature of the anode electrode 24 locally increases due to the supply of energy to the anode electrode 24 from the anode-electrode driving circuit 37, an occluded gas inside the anode electrode 24 is released or a material constituting the anode electrode 24 is evaporated, and such releasing or evaporation grows to be large-scale discharges (for example, spark discharges).
For displaying an image on the display, a positive voltage VG-SL (for example, 160 volts) is applied to a gate electrode (to be referred to as xe2x80x9cselected gate electrodexe2x80x9d hereinafter) constituting a pixel that is to emit lit. On the other hand, a voltage VG-NSL (for example, 0 volt) is applied to a gate electrode (to be referred to as xe2x80x9cnon-selected gate electrodexe2x80x9d hereinafter) constituting a pixel that is not to emit light. Further, a voltage VC-SL (for example, a voltage of at least 0 volt but less than 30 volts depending upon brightness) is applied to a cathode electrode (to be referred to as xe2x80x9cselected cathode electrodexe2x80x9d hereinafter) constituting the pixel that is to emit light. On the other hand, a voltage VC-NSL (for example, 30 volts) is applied to a cathode electrode (to be referred to as xe2x80x9cnon-selected cathode electrodexe2x80x9d hereinafter) constituting the pixel that is not to emit light. Therefore, in a pixel that emits light in the highest brightness, there is a voltage difference of 160 volts between the cathode electrode 12 and the anode electrode 14, and in a darkest pixel, there is a voltage difference of 130 volts between the cathode electrode 12 and the gate electrode 14. FIG. 84A schematically shows the above state. A voltage to be applied to the gate electrode 14 is shown as xe2x80x9cVgxe2x80x9d, and a voltage to be applied to the cathode electrode 12 is shown as xe2x80x9cVCxe2x80x9d. The voltage in the anode electrode 24 is maintained at 5 kV. FIG. 85A shows potentials of the selected gate electrode and the selected cathode electrode in the above state. In FIGS. 85A, 85B and 86, a blank triangle shows one example of potential of a cathode electrode, a blank circle, a solid circle and a blank square show examples of potentials of a gate electrode, and a solid triangle shows one example of an anode electrode.
When it is now supposed that a discharge starts to take place between the anode electrode 24 and the gate electrode 14, the potential of the gate electrode 14 increases with the elapse of time and ultimately increases up to a voltage Vxe2x80x3G close to the potential of the anode electrode 24. The potential of the gate electrode 14 is readily transmitted to the gate-electrode driving circuit 31 and may possibly damage the gate-electrode driving circuit 31. Further, as a result of an increase in the potential of the gate electrode 14 with the elapse of time, a voltage difference between the cathode electrode 12 and the gate electrode 14 increases, an excess current of emitted-electrons flows from the electron emission electrode 16A, and a discharge also takes place between the electron emission electrode 16A and the gate electrode 14 or between the electron emission electrode 16A and the anode electrode 24, which causes permanent damage on the gate electrode 14 and/or the electron emission electrode 16A. Further, when a discharge takes place between the gate electrode 14 having an increased potential and the electron emission electrode 16A, the potential of the cathode electrode 12 increases, and such a potential Vxe2x80x3c is readily transmitted to the cathode-electrode driving circuit 34 and may possibly damage the cathode-electrode driving circuit 34. FIG. 84B schematically shows the above state. Further, FIG. 85B schematically shows potentials of the selected gate electrode and the selected cathode electrode in the above state, and FIG. 86 schematically shows a change in potential in the selected gate electrode. In FIG. 85B and 86, t0 shows a time period (approximately 2 microseconds) that passes from the start of a discharge to the start of an increase of potential of the gate electrode, t1 shows a time period (approximately 3 microseconds) that passes from the start of the discharge to a time when the potential of the gate electrode comes to be approximately 170 volts, and t2 shows a time period (approximately 5 microseconds) from the start of the discharge to a time when the potential of the gate electrode comes to be approximately 2 kV.
For inhibiting a discharge between the anode electrode 24 and the gate electrode 14, it is effective to inhibit the emission of electrons and ions that work as a trigger of the discharge, and for that purpose, it is required to control particles strictly. It involves high technical difficulties to carry out the above particle control in the process for producing the first panel or a display having the first panel.
It is therefore an object of the present invention to provide a flat-type display that permits reliable inhibition of discharges between the first panel and the second panel, so that display images on a screen are free from degradation.
According to a first aspect of the present invention, the above object is achieved by a flat-type display comprising a first panel having electron-emitting portions; a second panel having an electron irradiation surface; and an electron-emitting-portion driving circuit for driving the electron-emitting portions, wherein an electron-emitting-portion cutoff circuit is provided between the electron-emitting portions and the electron-emitting-portion driving circuit for preventing a discharge between the electron-emitting portions and the electron irradiation surface. In the flat-type display of the present invention, a closed space between the first panel and the second panel constitutes a vacuum space. The first panel and the second panel are bonded to each other in their circumferential portions through a frame or without any frame.
In the flat-type display according to the first aspect of the present invention, preferably, a first predetermined voltage VPD1 is applied to the electron-emitting-portion cutoff circuit, and when the potential of an electron-emitting portion connected to the electron-emitting-portion cutoff circuit comes to be a second predetermined voltage VPD2 due to a discharge between the electron-emitting portion and the electron irradiation surface, the electron-emitting-portion cutoff circuit operates on the basis of a voltage difference (VPD2xe2x88x92VPD1) between the first predetermined voltage and the second predetermined voltage. In this case, desirably, in view of preventing the breakdown of the electron-emitting-portion driving circuit, |VOUT-MAXxe2x88x92VPD1| less than VCOLAPSE is satisfied in which VCOLAPSE is a breakdown voltage of the electron-emitting-portion driving circuit and VOUT-MAX is a maximum value of an output voltage of the electron-emitting-portion driving circuit. Otherwise, desirably, in view of preventing the breakdown of the electron-emitting-portion driving circuit, |VOUT-MAXxe2x88x92VPD1| less than REMISSIONxc2x7ICOLAPSE is satisfied in which ICOLAPSE is a breakdown current of the electron-emitting-portion driving circuit and REMISSION is a resistance value between the electron-emitting-portion driving circuit and the electron-emitting portion.
In the flat-type display according to the first aspect of the present invention, preferably, the second panel comprises a substrate, phosphor layers and an anode electrode. In this case, further, it is preferred to employ a constitution in which an anode-electrode driving circuit is further provided and an anode-electrode cutoff circuit is provided between the anode electrode and the anode-electrode driving circuit for preventing a discharge between the electron-emitting portion and the electron irradiation surface. The constitution of the anode-electrode cutoff circuit can be the same as that of an anode-electrode cutoff circuit in a flat-type display according to a second aspect of the present invention.
According to a second aspect of the present invention, the above object is achieved by a flat-type display comprising a first panel having electron-emitting portions; a second panel having an electron irradiation surface composed of phosphor layers and an anode electrode; and an anode-electrode driving circuit for driving the anode electrode, wherein an anode-electrode cutoff circuit is provided between the anode electrode and the anode-electrode driving circuit for preventing a discharge between the electron-emitting portions and the electron irradiation surface.
In the flat-type display according to the second aspect of the present invention, preferably, when no discharge takes place between the electron-emitting portion and the electron irradiation surface, the anode-electrode cutoff circuit is in a non-operated state, and when a discharge takes place between the electron-emitting portion and the electron irradiation surface, the anode-electrode cutoff circuit operates. Further, preferably, the anode-electrode cutoff circuit operates on the basis of an electric current that flows between the anode electrode and the anode-electrode driving circuit due to a discharge between the electron-emitting portion and the electron irradiation surface.
The anode electrode may have a constitution in which an effective field is covered with an electrically conductive material having the form of one sheet or may have a constitution in which the anode electrode is constituted of anode electrode units that correspond individually to one or a plurality of electron-emitting portions or correspond individually to one or a plurality of pixels. When the anode electrode has the former constitution, it is sufficient to provide one anode-electrode cutoff circuit. When the anode electrode has the latter constitution, it is sufficient to provide the anode-electrode cutoff circuits in a number equal to the number of the units, or it is sufficient to employ a constitution in which the anode electrode units are connected through one wiring and one anode-electrode cutoff circuit is connected to the wiring.
According to a third aspect of the present invention, the above object is achieved by a flat-type display comprising a first panel having electron-emitting portions; a second panel having an electron irradiation surface; an electron-emitting-portion driving circuit for driving the electron-emitting portions; a shield member disposed between the electron-emitting portions and the electron irradiation surface; and a shield-member voltage-applying means for applying a voltage to the shield member, wherein a shield-member cutoff circuit is provided between the shield member and the shield-member voltage-applying means for preventing a discharge between the shield member and the electron irradiation surface.
In the flat-type display according to the third aspect of the present invention, the shield member may be provided with a function as a so-called focus electrode. The shield member may have a constitution in which an effective field is covered with an electrically conductive material having the form of one sheet or may have a constitution in which the shield member is constituted of shield member units that correspond individually to one or a plurality of electron-emitting portions or correspond individually to one or a plurality of pixels. When the shield member has the former constitution, it is sufficient to provide one shield-member cutoff circuit. When the shield member has the latter constitution, it is sufficient to provide the shield-member cutoff circuits in a number equal to the number of units, or there may be employed a constitution in which the units are connected through one wiring and the shield-member cutoff circuit is connected to the wiring. The focus electrode refers to an electrode for converging the paths of electrons emitted from the electron-emitting portions toward the electron irradiation surface of the second panel so that brightness may be improved and that an optical crosstalk between neighboring pixels may be prevented. For allowing the shield member to work as a focus electrode, a relatively negative voltage is applied to the shield member from the shield-member voltage-applying means. The shield member may be provided integrally with the electron-emitting portions, or it may be provided separately from the electron-emitting portions. The shield member is required to have opening portions formed in advance for passing electrons emitted from the electron-emitting portions. Such opening portions may have a constitution in which one opening portion corresponds to one electron-emitting portion or one opening portion corresponds to a plurality of the electron-emitting portions.
In the flat-type display according to the third aspect of the present invention, preferably, the second panel comprises a substrate, phosphor layers and an anode electrode. In this case, it is preferred to employ a constitution in which an anode-electrode driving circuit is further provided and an anode-electrode cutoff circuit is provided between the anode electrode and the anode-electrode driving circuit for preventing a discharge between the shield member and the electron irradiation surface. The constitution of the anode-electrode cutoff circuit can be the same as that of the anode-electrode cutoff circuit of the flat-type display according to the second aspect of the present invention. Otherwise, the electron-emitting-portion cutoff circuit in the flat-type display according to the first aspect of the present invention may be incorporated into the flat-type display according to the third aspect of the present invention.
The flat-type display according to any one of the first to third aspects of the present invention (these flat-type displays will be sometimes generally referred to as xe2x80x9cflat-type display of the present inventionxe2x80x9d hereinafter) may have a constitution in which a stripe-shaped gate electrode and a stripe-shaped cathode electrode extending in a direction different from the extending direction of the stripe-shaped gate electrode are provided, the electron-emitting portion is formed in an overlap region where a projection image of the stripe-shaped gate electrode and a projection image of the stripe-shaped cathode electrode overlap, the electron-emitting-portion driving circuit comprises a first driving circuit connected to the gate electrode and a second driving circuit connected to the cathode electrode, and the first driving circuit is connected to the gate electrode through the electron-emitting-portion cutoff circuit. The flat-type display having the above constitution will be referred to as xe2x80x9cflat-type display according to the first constitution of the present inventionxe2x80x9d for convenience.
Alternatively, the flat-type display of the present invention may have a constitution in which a stripe-shaped gate electrode and a stripe-shaped cathode electrode extending in a direction different from the extending direction of the stripe-shaped gate electrode are provided, the electron-emitting portion is formed in an overlap region where a projection image of the stripe-shaped gate electrode and the stripe-shaped cathode electrode overlap, the electron-emitting-portion driving circuit comprises a first driving circuit connected to the gate electrode and a second driving circuit connected to the cathode electrode, and the second driving circuit is connected to the cathode electrode through the electron-emitting-portion cutoff circuit. The flat-type display having the above constitution will be referred to as xe2x80x9cflat-type display according to the second constitution of the present inventionxe2x80x9d for convenience.
In the flat-type display according to the first or second constitution of the present invention, preferably, when no discharge takes place between the electron-emitting portion and the electron irradiation surface, the electron-emitting-portion cutoff circuit is in a non-operated state, and when a discharge takes place between the electron-emitting portion and the electron irradiation surface, the electron-emitting-portion cutoff circuit operates.
The flat-type display of the present invention may have a constitution in which a stripe-shaped gate electrode and a stripe-shaped cathode electrode extending in a direction different from the extending direction of the stripe-shaped gate electrode are provided, the electron-emitting portion is formed in an overlap region where a projection image of the stripe-shaped gate electrode and a projection image of the stripe-shaped cathode electrode overlap, the electron-emitting-portion driving circuit comprises a first driving circuit connected to the gate electrode and a second driving circuit connected to the cathode, and the electron-emitting-portion cutoff circuit comprises a first cutoff circuit provided between the gate electrode and the first driving circuit and a second cutoff circuit provided between the cathode electrode and the second driving circuit. The flat-type display having the above constitution will be referred to as xe2x80x9cflat-type display according to the third constitution of the present inventionxe2x80x9d for convenience.
In the flat-type display according to the third constitution of the present invention, preferably, when no discharge takes place between the electron-emitting portion and the electron irradiation surface, the first and second cutoff circuits are in a non-operated state, and when a discharge takes place between the electron-emitting portion and the electron irradiation surface, the first cutoff circuit operates, and the second cutoff circuit operates on the basis of operation of the first cutoff circuit.
The flat-type display according to the first, second or third constitution of the present invention may have a structure in which the first panel has a plurality of cold cathode field emission devices,
each cold cathode field emission device comprises;
(a) a support member,
(b) a cathode electrode formed on the support member,
(c) an insulating layer formed on the support member and the cathode electrode,
(d) a gate electrode formed on the insulating layer,
(e) an opening portion formed through the gate electrode and the insulating layer, and
(f) an electron emission electrode formed on a portion of the cathode electrode which portion is positioned in the bottom portion of the opening portion, and
the electron emission electrode exposed in the bottom portion of the opening portion corresponds to the electron-emitting portion.
The cold cathode field emission device having the above structure will be referred to as xe2x80x9ccold cathode field emission device having the first structurexe2x80x9d for convenience. The above cold cathode field emission device includes a Spindt-type (cold cathode field emission device in which a conical electron emission electrode is formed on a portion of the cathode electrode which portion is positioned in the bottom portion of the opening portion), a crown-type (cold cathode field emission device in which a crown-shaped electron emission electrode is formed on a portion of the cathode electrode which portion is positioned in the bottom portion of the opening portion) and a plane-type (cold cathode field emission device in which a nearly flat-surface electron emission electrode is formed on a portion of the cathode electrode which portion is positioned in the bottom portion of the opening portion).
Alternatively, the flat-type display according to the first, second or third constitution of the present invention may have a structure in which the first panel has a plurality of cold cathode field emission devices,
each cold cathode field emission device comprises;
(a) a support member,
(b) a cathode electrode formed on the support member,
(c) an insulating layer formed on the support member and the cathode electrode,
(d) a gate electrode formed on the insulating layer, and
(e) an opening portion that is formed through the gate electrode and the insulating layer and has a bottom portion where the cathode electrode is exposed, and
a portion of the cathode electrode which portion is exposed in the bottom portion of the opening portion corresponds to the electron-emitting portion.
The cold cathode field emission device having the above structure will be referred to as xe2x80x9ccold cathode field emission device having the second structurexe2x80x9d for convenience. The above cold cathode field emission device includes a flat-type cold cathode field emission device that emits electrons from the flat surface of the cathode electrode, and a crater-type cold cathode field emission device that emits electrons from a convex portion of the surface of the cathode electrode having a convexo-concave shape.
Further, the flat-type display according to the first, second or third constitution of the present invention may have a structure in which the first panel has a plurality of cold cathode field emission devices,
each cold cathode field emission device comprises;
(a) a support member,
(b) a cathode electrode which is formed on or above the support member and has an edge portion,
(c) an insulating layer formed at least on the cathode electrode,
(d) a gate electrode formed on the insulating layer, and
(e) an opening portion formed through at least the gate electrode and the insulating layer, and
the edge portion of the cathode electrode which edge portion is exposed on the bottom portion or the side wall of the opening portion corresponds to the electron-emitting portion.
The cold cathode field emission device having the above structure will be referred to as a cold cathode field emission device having the third structure or an edge-type cold cathode field emission device.
Further, the flat-type display according to the first, second or third constitution of the present invention may have a structure in which the first panel has a plurality of cold cathode field emission devices,
each cold cathode field emission device comprises;
(a) a stripe-shaped spacer made of an insulating material and formed on a support member,
(b) a gate electrode made of a stripe-shaped material layer having a plurality of opening portions, and
(c) an electron-emitting portion, and
the stripe-shaped material layer is arranged to come in contact with the top surface of the spacer and to position the opening portion above the electron-emitting portion.
The cold cathode field emission device having the above structure will be referred to as xe2x80x9ccold cathode field emission device having the fourth structurexe2x80x9d for convenience. The electron emission electrode or the electron-emitting portion in the cold cathode field emission device having any one of the first to third structures can be applied to the electron-emitting portion of the cold cathode field emission device having the fourth structure.
The electron-emitting-portion driving circuit, the first driving circuit and the second driving circuit for driving the electron-emitting portion can be circuits having known constitutions. Further, the anode-electrode driving circuit and the shield-member voltage-applying means can be circuits having known constitutions.
The electron-emitting-portion cutoff circuit, the first cutoff circuit and the second cutoff circuit in the flat-type display according to the first aspect of the present invention and the shield-member cutoff circuit in the flat-type display according to the third aspect of the present invention can be any one, for example, of MOS-type FET (field-effect transistor), a combination of MOS-type FET and a diode, a combination of n-channel MOS-type and p-channel MOS-type FET, a combination of n-channel MOS-type, p-channel MOS-type FET and a diode, TFT (thin film transistor), a combination of TFT and a diode, a combination of n-channel type TFT and p-channel type TFT, a combination of n-channel type TFT, p-channel type TFT and a diode, and a combination of these with a resistance element. The TFT includes a bottom gate type and a top gate type.
Alternatively, the electron-emitting-portion cutoff circuit, the first cutoff circuit and the second cutoff circuit in the flat-type display according to the first aspect of the present invention and the shield-member cutoff circuit in the flat-type display according to the third aspect of the present invention include a discharge tube and a Zener diode. For preventing a malfunction, preferably, the voltage difference for bringing the discharge tube or the Zener diode into continuity is greater than a voltage difference between a maximum value of output voltage of the driving circuit to which the discharge tube or the Zener diode is connected and the first predetermined voltage VPD1 and is greater than a voltage difference between a minimum value of output voltage of the driving circuit to which the discharge tube or the Zener diode is connected and the first predetermined voltage VPD1.
In the flat-type display according to the second aspect of the present invention, the anode-electrode cutoff circuit includes a combination of MOS-type FET and a resistance element.
The electron-emitting-portion cutoff circuit, the first cutoff circuit, the second cutoff circuit or the shield-member cutoff circuit may be incorporated, for example, into the first panel, or may be incorporated into the electron-emitting-portion driving circuit, the first driving circuit, the second driving circuit or the shield-member voltage-applying means. When the electron-emitting-portion cutoff circuit, the first cutoff circuit, the second cutoff circuit or the shield-member cutoff circuit is incorporated into the first panel, each may be disposed in an ineffective field (field which is outside the effective field that works as an actual display screen and which is inside the vacuum space), or each may be disposed outside the frame.
The anode-electrode cutoff circuit or the shield-member cutoff circuit may be incorporated, for example, into the second panel, or the anode-electrode cutoff circuit may be incorporated into the anode-electrode driving circuit. When the anode-electrode cutoff circuit is incorporated into the second panel, it may be disposed in the ineffective field or outside the frame.
In the flat-type display of the present invention, the electron-emitting-portion cutoff circuit, the first cutoff circuit, the second cutoff circuit, the anode-electrode cutoff circuit or the shield-member cutoff circuit may be provided with a kind of a timer for continuing its operation for a predetermined period of time once it starts its operation. The timer includes a multi-vibrator.
The material for constituting the cold cathode field emission device having the first, second or third structure or the material for constituting the shield member includes at least one metal selected from the group consisting of tungsten (W), niobium (Nb), tantalum (Ta), titanium (Ti), molybdenum (Mo), chromium (Cr), aluminum (Al), copper (Cu), gold (Au), silver (Ag), nickel (Ni), cobalt (Co), zirconium (Zr), iron (Fe), platinum (Pt) and zinc (Zn); alloys or compounds containing these metal elements (for example, nitrides such as TiN and silicides such as WSi2, MoSi2, TiSi2, TaSi2, etc.); a semiconductor material such as silicon (Si); and electrically conductive metal oxides such as ITO (indium tin oxide), indium oxide and zinc oxide. When the gate electrode is formed, a thin film made of the above material is formed on the insulating layer by a known thin film forming method such as a CVD method, a sputtering method, a vapor deposition method, an ion plating method, an electrolytic plating method, an electroless plating method, a screen printing method, a laser abrasion method or a sol-gel method. When the thin film is formed on the entire surface of the insulating layer, the thin film is patterned by a known patterning method, to form the stripe-shaped gate electrode. The opening portion may be formed in the gate electrode after the formation of the stripe-shaped gate electrode, or the opening portion may be formed in the gate electrode concurrently with the formation of the stripe-shaped gate electrode. Further, if a patterned resist is formed on the insulating layer before the formation of the electrically conductive material layer for the gate electrode, the gate electrode can be formed by a lift-off method. Further, if vapor deposition is carried out using a mask having an opening having the form corresponding to the form of the gate electrode, or if screen printing is carried out with a screen having such an opening, the patterning after the formation of the thin film is no longer necessary. Further, the gate electrode may be formed by preparing a stripe-shaped material layer having an opening portion in advance and fixing such a stripe-shaped material layer on the spacer, whereby the cold cathode field emission device having the fourth structure can be obtained.
In the cold cathode field emission device having the first structure which device is a Spindt-type cold cathode field emission device, the material for the electron emission electrode includes tungsten, tungsten alloy, molybdenum, molybdenum alloy, titanium, titanium alloy, niobium, niobium alloy, tantalum, tantalum alloy, chromium, chromium alloy and silicon containing an impurity (polysilicon and amorphous silicon). These materials may be used alone or in combination.
In the cold cathode field emission device having the first structure which device is a crown-type field emission device, the material for the electron emission electrode includes electrically conductive particles and a combination of electrically conductive particles with a binder. The material of the electrically conductive particles includes carbon-containing materials such as graphite; refractory metals such as tungsten (W), niobium (Nb), tantalum (Ta), titanium (Ti), molybdenum (Mo) and chromium (Cr); and transparent electrically conductive materials such as ITO (indium tin oxide). The binder includes glass such as water glass and general purpose resins. Examples of the general purpose resins include thermoplastic resins such as a vinyl chloride resin, a polyolefin resin, a polyamide resin, a cellulose ester resin and a fluorine resin, and thermosetting resins such as an epoxy resin, an acrylic resin and a polyester resin. For improving electron emission efficiency, preferably, the particle size of the electrically conductive particles is sufficiently small as compared with dimensions of the electron-emitting portion. Although not specially limited, the form of the electrically conductive particles is spherical, polyhedral, plate-like, acicular, columnar or amorphous. Preferably, the electrically conductive particles have such a form that exposed portions formed by the particles form acute projections. Electrically conductive particles having different dimensions and different forms may be used as a mixture.
In the cold cathode field emission device having the first structure which device is a plane-type field emission device, preferably, the electron emission electrode is composed of a material having a smaller work function "PHgr" than a material for the cathode electrode. The material for the electron emission electrode can be selected on the basis of the work function of a material for the cathode electrode, a voltage difference between the gate electrode and the cathode electrode, a required current density of emitted electrons, and the like. Typical examples of the material for the cathode electrode of the cold cathode field emission device include tungsten ("PHgr"=4.55 eV), niobium ("PHgr"=4.02-4.87 eV), molybdenum ("PHgr"=4.53-4.95 eV), aluminum ("PHgr"=4.28 eV), copper ("PHgr"=4.6 eV), tantalum ("PHgr"=4.3 eV), chromium ("PHgr"=4.5 eV) and silicon ("PHgr"=4.9 eV). The material for the electron emission electrode preferably has a smaller work function "PHgr" than these materials, and the value of the work function thereof is preferably approximately 3 eV or smaller. Examples of such a material include carbon ("PHgr" less than 1 eV), cesium ("PHgr"=2.14 eV), LaB6 ("PHgr"=2.66-2.76 eV), BaO ("PHgr"=1.6-2.7 eV), SrO ("PHgr"=1.25-1.6 eV), Y2O3 ("PHgr"=2.0 eV), CaO ("PHgr"=1.6-1.86 eV), BaS ("PHgr"=2.05 eV), TiN ("PHgr"=2.92 eV) and ZrN ("PHgr"=2.92 eV). More preferably, the electron emission electrode is formed of a material having a work function "PHgr" of 2 eV or lower. The material for the electron emission electrode is not necessarily required to have electric conductivity.
As a material for the electron-emitting portion, particularly, carbon is preferred. More specifically, diamond is preferred, and above all, amorphous diamond is preferred. When the electron emission electrode is formed of amorphous diamond, an emitted electron current density necessary for a flat-panel display can be obtained at an electric field intensity of 5xc3x97107 V/m or lower. Further, since amorphous diamond is an electric resister, emitted electron currents obtained from the electron emission electrodes can be brought into uniform currents, and the fluctuation of brightness can be therefore suppressed when such field emission devices are incorporated into a flat-panel display. Further, since the amorphous diamond exhibits remarkably high durability against sputtering by ions of residual gas in the flat-panel display, cold cathode field emission devices having a longer lifetime can be attained.
Otherwise, in the cold cathode field emission device having the first structure which device is a plane-type cold cathode field emission device, the material for the electron emission electrode can be selected from materials which have a secondary electron gain xcex4 greater than the secondary electron gain xcex4 which the electrically conductive material for the cathode electrode has. That is, the above material can be properly selected from metals such as silver (Ag), aluminum (Al), gold (Au), cobalt (Co), copper (Cu), molybdenum (Mo), niobium (Nb), nickel (Ni), platinum (Pt), tantalum (Ta), tungsten (W) and zirconium (Zr); semiconductors such as silicon (Si) and germanium (Ge); inorganic simple substances such as carbon and diamond; and compounds such as aluminum oxide (Al2O3), barium oxide (BaO), beryllium oxide (Beo), calcium oxide (CaO), magnesium oxide (MgO), tin oxide (SnO2), barium fluoride (BaF2) and calcium fluoride (CaF2). The material for the electron emission electrode is not necessarily required to have electric conductivity.
In the cold cathode field emission device having the second structure (flat-type cold cathode field emission device or crater-type cold cathode field emission device) or the cold cathode field emission device having the third structure (edge-type cold cathode field emission device), the material for the cathode electrode corresponding to the electron-emitting portion can be selected from metals such as tungsten (W), tantalum (Ta), niobium (Nb), titanium (Ti), molybdenum (Mo), chromium (Cr), aluminum (Al), copper (Cu), gold (Au) and silver (Ag); alloys and compounds of these metals (for example, nitrides such as TiN and silicides such as WSi2, MoSi2, TiSi2 and TaSi2); semiconductors such as diamond; and a thin carbon film. Although not specially limited, the thickness of the above cathode electrode is in the range of from approximately 0.05 to 0.5 xcexcm, preferably 0.1 to 0.3 xcexcm. The method for forming the cathode electrode includes deposition methods such as an electron beam deposition method and a hot filament deposition method, a sputtering method, a combination of a CVD method or an ion plating method with an etching method, a screen-printing method and a plating method. When a screen-printing method or a plating method is employed, the cathode electrodes in the form of stripes can be directly formed.
Otherwise, in the cold cathode field emission device having the second structure (flat-type cold cathode field emission device or crater-type cold cathode field emission device), the cold cathode field emission device having the third structure (edge-type cold cathode field emission device) or the cold cathode field emission device having the first structure which device is a plane-type cold cathode field emission device, the cathode electrode or the electron emission electrode can be formed from an electrically conductive paste prepared by dispersing electrically conductive fine particles. Examples of the electrically conductive fine particles include a graphite powder; a graphite powder mixed with at least one of a barium oxide powder, a strontium oxide powder or a metal powder; diamond particles or a diamond-like carbon powder containing an impurity such as nitrogen, phosphorus, boron or triazole; a carbon-nano-tube powder; an (Sr, Ba, Ca)CO3 powder; and a silicon carbide powder. It is particularly preferred to select a graphite powder as electrically conductive fine particles in view of a decrease in threshold electric field and an improvement in durability of the electron-emitting portion. The electrically conductive fine particles may have the form of spheres or scales, or they may have a fixed or amorphous form. The particle diameter of the electrically conductive fine particles is not critical so long as it is equal to, or less than, the thickness or the pattern width of the cathode electrode or the electron emission electrode. With a decrease in the above particle diameter, the number of electrons emitted per unit area can be increased. When the above particle diameter is too small, however, the cathode electrode or the electron emission electrode may deteriorate in electric conductivity. The above particle diameter is therefore preferably in the range of from approximately 0.01 to 4.0 xcexcm. Such electrically conductive fine particles are mixed with a glass component or other proper binder to prepare an electrically conductive paste, a desired pattern of the electrically conductive paste is formed by a screen-printing method and the pattern is calcined, whereby the cathode electrode which works as an electron-emitting portion or the electron emission electrode can be formed. Otherwise, the cathode electrode which works as an electron-emitting portion or the electron emission electrode can be formed by a combination of a spin coating method with an etching method or by a lift-off method.
In the cold cathode field emission device having the first structure which device is a Spindt-type field emission device or a crown-type field emission device, the material for the cathode electrode can be selected from metals such as tungsten (W), niobium (Nb), tantalum (Ta), molybdenum (Mo), chromium (Cr), aluminum (Al) and copper (Cu); alloys and compounds of these metals (for example, nitrides such as TiN and silicides such as WSi2, MoSi2, TiSi2 and TaSi2); semiconductors such as silicon (Si); and ITO (indium-tin oxide). The method for forming the cathode electrode includes deposition methods such as an electron beam deposition method and a hot filament deposition method, a sputtering method, a combination of a CVD method or an ion plating method with an etching method, a screen-printing method, a plating method and a lift-off method. When a screen-printing method or a plating method is employed, the cathode electrodes in the form of stripes can be directly formed.
In the flat-type display of the present invention including the flat-type display according to any one of the first to third constitutions or the flat-type display having the cold cathode field emission device having any one of the first to third structures, preferably, the second panel comprises a substrate, phosphor layers and an anode electrode. The electron irradiation surface is formed of phosphor layers or an anode electrode depending upon the structure of the second panel.
The material for the anode electrode can be selected depending upon the constitution of the flat-type display. That is, when the flat-type display is a transmission type (the second panel corresponds to a display screen) and when the anode electrode and the phosphor layer are stacked on the substrate in this order, not only the substrate but also the anode electrode itself are required to be transparent, and a transparent electrically conductive material such as ITO (indium-tin oxide) is used. When the flat-type display is a reflection type (the first panel corresponds to a display screen), or when the cold cathode field emission is a transmission type but when the phosphor layer and the anode electrode are stacked on the substrate in this order, not only ITO can be used, but also the material can be selected from those materials which are discussed with regard to the cathode electrode and the gate electrode.
The phosphor material for the phosphor layer can be selected from a fast-electron-excitation type phosphor material or a slow-electron-excitation type phosphor material. When the flat-type display is a monochrome display, it is not required to pattern the phosphor layer. When the flat-type display is a color display, preferably, the phosphor layers corresponding to three primary colors of red (R), green (G) and blue (B) patterned in the form of stripes or dots are alternately arranged. A black matrix may be filled in a gap between one patterned phosphor layer and another phosphor layer for improving a display screen in contrast.
Examples of the constitution of the anode electrode and the phosphor layer include (1) a constitution in which the anode electrode is formed on the substrate and the phosphor layer is formed on the anode electrode and (2) a constitution in which the phosphor layer is formed on the substrate and the anode electrode is formed on the phosphor layer. In the above constitution (1), a so-called metal back film electrically connected to the anode electrode may be formed on the phosphor layer. In the above constitution (2), the metal back layer may be formed on the anode electrode.
Preferably, the projection image of the stripe-shaped gate electrode and the projection image of the stripe-shaped cathode electrode extend in directions so as to cross each other at right angles, since the flat-type display can be structurally simplified. The electron-emitting portion (one or a plurality of cold cathode field emission devices) is formed in an overlap region where the projection images of stripe-shaped cathode electrode and the stripe-shaped gate electrode overlap (the region corresponding to a region for one pixel or a region for one sub-pixel). Generally, such overlap regions are arranged in the form of a two-dimensional matrix in the effective field of the first panel (region which works as an actual display screen).
In the cold cathode field emission device having any one of the first to third structures, the opening portion (form obtained by cutting the opening portion with an imaginary plane in parallel with the surface of the support member) may have any arbitrary form such as a circle, an ellipse, a rectangular or square form, a polygon, a roundish rectangular or square form or a roundish polygon. The opening portion can be formed, for example, by an isotropic etching method or a combination of anisotropic and isotropic etching methods. There may be employed a constitution in which one opening portion is formed in the gate electrode, one opening portion communicating with the one opening portion formed in the gate electrode is formed in the insulating layer and one or a plurality of the electron emission electrodes are formed in the opening portion formed in the insulating layer. Otherwise, there may be also employed a constitution in which a plurality of the opening portions are formed in the gate electrode, one opening portion communicating with such opening portions is formed in the insulating layer and one or a plurality of the electron emission electrode are formed in the opening portion formed in the insulating layer.
The material for the insulating layer includes SiO2, SiN, SiON, SOG (spin on glass), a low-melting glass and a glass paste. These materials may be used alone or in combination as required. The insulating layer can be formed by a known method such as a CVD method, an application method, a sputtering method or a printing method.
The insulating layer may be formed in the form of a separation wall. In this case, the insulating layer in the form of a separation wall is formed in a region between one stripe-shaped cathode electrode and another stripe-shaped cathode electrode which are adjacent to each other, or when a plurality of the cathode electrodes are taken as one group, the insulating layer can be formed in a region between one group and another group which are adjacent to each other. The material for the insulating layer in the form of a separation wall can be selected from known electrically insulating materials. For example, a material prepared by mixing a generally used low-melting glass with a metal oxide such as alumina can be used. The insulating layer in the form of a separation wall can be formed, for example, by a screen-printing method, a sandblasting method, a dry film method or a photosensitive method. The dry film method refers to a method in which a photosensitive film is laminated on the support member, the photosensitive film in portions where the insulating layer in the form of a separation wall are to be formed is removed by exposure and development, an insulating layer material is filled in opening portions formed by the removal of the photosensitive film, and calcining of the insulating layer material is carried out. The photosensitive film is combusted and removed by the calcining, and the insulating layer material which is filled in the opening portions remains to form the insulating layer in the form of a separation wall. The photosensitive method refers to a method in which a photosensitive insulating layer material for forming a separation wall is formed on the support member, the insulating layer material is patterned by exposure and development, and then calcining or sintering of the insulating layer material is carried out. The stripe-shaped spacer made of an insulating material in the cold cathode field emission device having the fourth structure can be also formed by the same method as the above.
A resistance layer may be formed between the cathode electrode and the electron emission electrode. Otherwise, when the surface of the cathode electrode or the edge portion of the cathode electrode corresponds to the electron-emitting portion, the cathode electrode may have a three-layered structure constituted of an electrically conductive material layer, a resistance layer and an electron-emitting layer corresponding to the electron-emitting portion. The resistance layer can stabilize performances of the cold cathode field emission device and can attain uniform electron-emitting properties. The material for the resistance layer includes carbon-containing materials such as silicon carbide (SiC); SiN; semiconductor materials such as amorphous silicon and the like; and refractory metal oxides such as ruthenium oxide (RuO2), tantalum oxide and tantalum nitride. The resistance layer can be formed by a sputtering method, a CVD method or a screen-printing method. The resistance value of the resistance layer is approximately 1xc3x97105 to 1xc3x97107 xcexa9, preferably several Mxcexa9.
The support member for constituting the first panel or the substrate for constituting the second panel may be any member or substrate so long as its surface is formed of an electrically insulating material. Examples thereof include a glass substrate, a glass substrate having a surface on which an insulating film is formed, a quartz substrate, a quartz substrate having a surface on which an insulating film is formed, and a semiconductor substrate having a surface on which an insulating film is formed.
When the first panel and the second panel are bonded to each other in their circumferential portions, they may be bonded with an adhesive layer or with a combination of a frame made of an insulating rigid material such as glass or ceramic with an adhesive layer. When the frame and the adhesive layer are used in combination, the facing distance between the first panel and the second panel can be adjusted to be larger by properly determining the height of the frame than that obtained when the adhesive layer alone is used. While a frit glass is generally used as a material for the adhesive layer, a so-called low-melting metal material having a melting point of approximately 120 to 400xc2x0 C. may be used. The low-melting metal material includes In (indium; melting point 157xc2x0 C.); an indium-gold low-melting alloy; tin (Sn)-containing high-temperature solders such as Sn80Ag20 (melting point 220 to 370xc2x0 C.) and Sn95Cug5 (melting point 227 to 370xc2x0 C.); lead (Pb)-containing high-temperature solders such as Pb97.5Ag2.5 (melting point 304xc2x0 C.), Pb94.5Ag5.5 (melting point 304-365xc2x0 C.) and Pb97.5Ag1.5Sn1.0 (melting point 309xc2x0 C.); zinc (Zn)-containing high-temperature solders such as Zn95Al5 (melting point 380xc2x0 C.); tin-lead-containing standard solders such as Sn5PB95 (melting point 300-314xc2x0 C.) and Sn2PB98 (melting point 316-322xc2x0 C.); and brazing materials such as Au88Ga12 (melting point 381xc2x0 C.) (all of the above subscript values show atomic %).
When three members of the first panel, the second panel and the frame are bonded, these three members may be bonded at the same time, or one of the first panel and the second panel may be bonded to the frame at a first stage and then the other of the first panel and the second panel may be bonded to the frame at a second stage. When bonding of the three members or bonding at the second stage is carried out in a high-vacuum atmosphere, a space surrounded by the first panel, the second panel, the frame and the adhesive layer comes to be a vacuum space upon bonding. Otherwise, after the three members are bonded, the space surrounded by the first panel, the second panel, the frame and the adhesive layer may be vacuumed to obtain a vacuum space. When the vacuuming is carried out after the bonding, the pressure in an atmosphere during the bonding may be any one of atmospheric pressure and reduced pressure, and the gas constituting the atmosphere may be ambient atmosphere or an inert gas containing nitrogen gas or a gas (for example, Ar gas) coming under the group O of the periodic table.
When the vacuuming is carried out after the bonding, the vacuuming can be carried out through a tip tube pre-connected to the first panel and/or the second panel. Typically, the tip tube is formed of a glass tube and is bonded to a circumference of a through hole formed in an ineffective field of the first panel and/or the second panel with a frit glass or the above low-melting metal material. After the space reaches a predetermined vacuum degree, the tip tube is sealed by thermal fusion. It is preferred to heat and then temperature-decrease the flat-type display as a whole before the sealing, since residual gas can be released into the space and can be removed out of the space by vacuuming.
In the flat-type display according to the first aspect of the present invention, the electron-emitting-portion cutoff circuit is provided between the electron-emitting portion and the electron-emitting-portion driving circuit for preventing a discharge between the electron-emitting portion and the electron irradiation surface. Even if a discharge takes place, therefore, the electron-emitting-portion cutoff circuit readily cuts off the electric connection between the electron-emitting portion and the electron-emitting-portion driving circuit. In the flat-type display according to the second aspect of the present invention, the anode-electrode cutoff circuit is provided between the anode electrode and the anode-electrode driving circuit for preventing a discharge between the electron-emitting portion and the electron irradiation surface. Even if a discharge takes place, therefore, the anode-electrode cutoff circuit readily cuts off the electric connection between the anode electrode and the anode-electrode driving circuit. In the flat-type display according to the third aspect of the present invention, the shield-member cutoff circuit is provided between the shield member and the shield-member voltage-applying means for preventing a discharge between the shield member and the electron irradiation surface. Even if a discharge takes place, therefore, the shield-member cutoff circuit readily cuts off the electric connection between the shield member and the shield-member voltage-applying means, so that no detrimental effect is caused on the shield-member voltage-applying means and further that no detrimental effect is caused on the electron-emitting portion and the electron-emitting-portion driving circuit.